Could Earth have sent life to Jupiter's moon Europa?

Could Earth have seeded Jupiter's moon Europa with bacterial life, where it could have taken hold in Europa's ocean and perhaps evolved into something more? That's the hypothesis of a new paper in the International Journal of Astrobiology by Zaza Osmanov of the Free University of Tbilisi in Georgia.

Osmanov calculates the chance that dust particles containing living bacteria were ejected from Earth's gravitational well and traveled to Jupiter's icy moon Europa, where they could have landed undestroyed and made their way through cracks in Europa's ice, beneath which lies a vast sea that scientists believe could harbor life.

The possibility of panspermia, bringing simple life to Earth from elsewhere in the universe, has been discussed for decades. Dust, meteoroids, asteroids and comets might all have contained life forms as they crashed into Earth.

The hypothesis is impossible to test experimentally, but in a paper published in the International Journal of Astronomy and Astrophysics , Osmanov, who is also affiliated with the E. Kharadze Georgian National Astrophysical Observatory, calls this the "reverse panspermia problem" and calculated that "in 5 billion years dust grains can travel in the interstellar medium at distances of the order of hundreds of parsecs."

Also, given the distribution of stars in the Milky Way, "particles emitted by every single planet will reach as many as 10 5 stellar systems." Moreover, Osmanov found that from a single planet, life can be transported to about a thousand star systems.

The red line is the trajectory of a dust grain traveling from Earth, at 1 astronomical unit (AU), to the vicinity of Jupiter at 5 AU, using the parameters and assumptions utilized in the text. Credit: Used with permission of Zaza Osmanov.

How the Europa case works

Using techniques similar to those in his earlier paper, Osmanov considered Earth as an origin of dust grains, and Europa, with its unique ice and ocean features, as their end point. Osmanov breaks his analysis into three parts:

Could dust grains carrying life have escaped Earth's gravitational field, and in what abundance?

Could such dust grains have landed on Europa in a way that didn't destroy them, and in what numbers? And 3. If they landed, could such grains have permeated Europa's thick crust of ice and reached its liquid surface?

Dust particles about a micron (a millionth of a meter) in size can contain packed bacteria of about the same size. Moreover, for the bacteria to survive any journey, their temperature cannot exceed about 300 Kelvin (about 27°C).

Dust grains are carried aloft by atmospheric turbulence; considering the energy imparted to one at 150 kilometers (93 miles) in altitude, as through a collision with cosmic dust, Osmanov's 2025 paper allowed him to calculate a maximum imparted velocity of the dust grain of 14 km/s at altitude, which exceeds Earth's escape velocity of 11.2 km/s.

More simple physics shows the particle would have a velocity of 8.4 km/s when far from Earth, about 10% faster than the International Space Station circles the planet. This would be happening for the entire 3.5 billion years that simple life has existed on Earth.

From Earth to Europa

After leaving Earth, three forces act on the dust particles: the pressure of radiation from the sun, the gravitational force of Jupiter (which dominates the sun's gravitational force after the grain has traveled about 97% of the sun-Jupiter distance), and the average drag force of the interplanetary medium in the solar system.

Osmanov solves the dust grain's equations of motion to find that its velocity at Jupiter is 20.1 km/s. The impact of the grain on Europa is at a maximum when it comes directly downward relative to the moon's surface. Using the dust grain's specific heat, he finds that only grains that come in at a very low angle—1 degree relative to the surface—will survive the impact, meaning only about three in a thousand bacteria packs survive the landing.

A flux of about one particle per square centimeter per second leaves Earth through a collision with cosmic dust in the atmosphere, or about 5 x 10 18 total particles per second, ejected equally in all directions. Using geometry to find the fraction of dust particles that enter Jupiter's gravitational zone, Osmanov finds that about 300 million such particles from Earth should reach Europa's surface every second. (Author's note: Much larger than I would have guessed!)

Besides those above, Osmanov uses two other results from the scientific literature: Bacteria that land on Europa's surface undergo "deactivation" in about 10,000 years, and about 20% to 40% of the moon's ice, which is 30 million to 80 million years old, undergoes fracturing from tidal heating and tidal friction from the titanic forces of Jupiter.

Simulations have found that regions of the ice can melt through in about 1,000 years, carrying bacteria down to the ocean surface, with broader holes tens of kilometers wide occurring i…